1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a system and method for forming silicon-containing films at low process temperatures using a high density plasma source.
2. Description of the Related Art
Conventional plasma-enhanced chemical vapor deposition (PECVD) processes using capacitively coupled plasma (CCP) plasma are suitable for the deposition of amorphous silicon (a-Si) thin films. These suitable for the deposition of amorphous silicon (a-Si) thin films. These conventional PECVD processes typically induce high hydrogen content into the film, necessitating a post-deposition thermal treatment to reduce the amount of hydrogen content.
Microcrystalline thin films with large sized grains are preferred for many applications. The carrier mobility of transistors fabricated with a-Si is poor, insufficient for LCD driver circuits. The carrier mobility is enhanced by using crystalline silicon thin films. A crystalline Si thin film provides significantly higher circuit performance, as compared to a-Si thin films.
The laser crystallization of a-Si thin film is often carried out to enhance the grain growth for high performance circuits. Sometimes impurities, such as Ni, are added in the a-Si thin films to enhance the laser crystallization kinetics. A high quality microcrystalline Si film, without impurities, is preferable for laser crystallization, as the step of incorporating any foreign impurities is eliminated. Impurity contamination can severely degrade the device performance. If the microcrystalline silicon film has a suitable crystallite size and high crystalline volume fraction, it can be used as a seed to achieve large grain growth by laser crystallization, without adding any impurities in the silicon film prior to laser crystallization.
High hydrogen dilution of the plasma is required to enhance the crystallite size in the deposited films. For this reasons, PECVD processes are often used. However, as mentioned above, there are also disadvantages associated with the use of a relatively high hydrogen concentration. These a-Si thin films require a high thermal budget dehydrogenation process prior to laser crystallization. These high thermal budget processes are not particularly suitable for Si deposition on low temperature substrates such as glass or plastic.
In general, hydrogen is required in the plasma, in addition to silicon precursor, to induce crystallization. The crystallite size and the microcrystalline volume fraction is enhanced in response to a more efficient and active hydrogen plasma. A high-density plasma process significantly enhances the plasma density and energy while minimizing the plasma damage. A more active hydrogen specie can significantly enhance the grain growth at lower temperatures.
It would be advantageous if low temperature processes could be developed for the deposition of a-Si thin films.
It would be advantageous if the thermal budget associated with the fabrication of microcrystalline films could be reduced through the development of a low hydrogen content deposition process. Such as process would lead to significant savings, by reducing the number of process steps, and enable the fabrication of novel device structures.
It would be advantageous if a low hydrogen content, low temperature PECVD process for the deposition of a-Si could be developed.
It would be advantageous if a lower temperature H2 ionization process could be developed for the deposition of microcrystalline Si films with a low hydrogen content, large crystallite size, and high volume fraction in the fabrication of high performance components for LCD devices integrated on low temperature substrates.